Method of producing a metal sheet by slip casting



Dec. 24, 1968 F. H. CLARK 3,418,114

METHOD OF PRODUCING A METAL SHEET BY SLIP CASTING Filed NOV. 28, 1967 INVENTOR fiazc'asjfliari ATTORNEYS United States Patent 3,418,114 METHOD OF PRODUCING A METAL SHEET BY SLIP CASTING Frances H. Clark, Summit, N.J., assignor to The Comstock Company, Higganum, Conn., a corporation of Connecticut Filed Nov. 28, 1967, Ser. No. 686,059 7 Claims. (Cl. 75-214) ABSTRACT OF THE DISCLOSURE This invention provides a mechanism and method for rapidly forming metallic sheets from metal powder by the procedure known as slip casting in the art of powder metallurgy.

In Patent 3,121,631, issued Feb. 18, 1964, in the name of Gregory J. Comstock as inventor is disclosed a method of forming metallic sheets, strips and other products which comprises forming a slip or bath which includes powdered metal in suspension and withdrawing from that bath a desired quantity, depositing that amount upon a support, removing the liquid content thereof, and thereafter utilizing heat and pressure to obtain the finished article. The slip or bath utilized as a medium for suspending the metal powder chosen as the starting material may be varied, in the practice of the process, as practical considerations direct.

A primary objective of the patented process is the production of thin metallic sheets, particularly sheets of metals difficult or impossible to obtain by conventional rolling procedures. The present invention has for its object the provision of a method whereby metallic sheets may be obtained by practicing the method just described, but somewhat more rapidly, and to an apparatus by means of which this increased rate of production may be obtained. Other economies are improved control over the width and thickness of the sheet.

The apparatus, which has a number of novel features, is rather diagrammatically illustrated in the accompanying drawing and the method practiced with its aid will be described.

An endless slip receiving member of desired length and width is indicated at 10 in the drawings, being supported by rollers 11 which may be suitably driven to advance the sheet at a chosen desired speed with its upper reach moving in the direction indicated by the arrow 12. This sheet is preferably of thin flexible metal, advantageously of stainless steel which is of somewhat porous character so as to receive and retain fluid chemical compounds applied to its surface. Such compounds are applied for the purpose of coagulating and stiffening the layer of the powdered metal slip, or suspension, deposited on the surface of the sheet so that it may readily be removed intact. The slip is deposited upon the moving screen at a point adjacent one end of its upper reach and removed by a pick-off devicesuch as the wedge-shaped member 13. It is then guided along a horizontal path toward stations at which it is processed further. The slip or suspension which includes the powdered metal issues from a precisely controlled elongated slot-like orifice in the bottom of the slip containing reservoir 14, this orifice extending transversely to the direction of movement of the screen and releasing in a constant stream the precise amount of suspension per unit of time which will insure that the layer of suspension deposited on the moving screen is of the desired thickness.

As each increment of such deposited suspension is moved by the screen toward the pick-oii member 13 it first passes between horizontal rollers 15, one of which is below the casting screen 10 and the second above that 3,418,114 Patented Dec. 24, 1968 screen, the rollers functioning to lightly press the liquid containing suspension so that some of its contained moisture is removed and caused to flow laterally and to escape over the lateral edges of the screen, a constant thickness of the layer of suspension being thus assured. After passing the rollers 15 the layer of suspension is subjected to a drying operation to remove the major portion of its remaining moisture, a drying lamp being diagrammatically illustrated at 16. It will be understood that any suitable drying means or device may be employed to perform the desired drying operation. Just prior to its removal from the casting screen the layer of suspension being processed is monitored by the thickness gauge 17 which controls by electronic feedback the orifice of the reservoir 14, this orifice being automatically adjusted to deliver more or less suspension per unit of time when the device 17 detects an undesirable variation in the thickness of the material on the screen.

After passing the pick-off device 13 the sheet of material being processed, which is still green or damp, passes between guide rollers and enters the sint-ering furnace 19 in which the binding or suspending substances originally employed in forming the slip are burned off so that the product which emerges is a porous metallic strip or sheet. When it is desired that the product shall be as dense as such a product may be made it is subjected tofurther rolling by passage through a rolling :mill 20, an annealing furnace 21, a second rolling mill 22 and a second annealing furnace 23.

The means for supplying slip or suspension of the precise character desired, in the desired quantities to the suspension reservoir 14 includes a bin 25 for powdered metal, a second bin 26 for the gel-forming binder which is then in the form of a dry powder, and a mixer 27 which measures quantities of these powders from bins 25 and 26 through the ducts or pipes diagrammatically illustrated. The mixed powders are then conducted to a wet mixer diagrammatically illustrated at 28 which receives measured amounts of distilled water from a source 24. The slip thus formed is passed through a pump 30 to a density transducer 31 and thence to the slip reservoir 14.

In passing from pump 30 to the density transducer 31 the slip moves through viscometer 32 which adjusts the viscosity of the slip by electronic feedback to a control valve 33 which regulates the flow of water from the source 24 to the wet mixer 28 so that the desired exact amount of distilled water entering the mixer is realized. The various mechanical and electrical instrumentalities mentioned are commercially obtainable, the details of construction of which form no part of the present invention although the combination described is novel and important.

The nature and amount of the dry powder supplied to the mixer 27 and the amount of water introduced into the wet mixture 28 determines the character of the suspension to be ultimately deposited upon the forming screen 10 and also determines the nature of the material applied to the forming screen for the purpose of coagulating and stiffening the layer of suspension or slip deposited upon that screen so that it may be more readily removed by the pick off device 13. The application of this material to the screen makes it possible to advance the screen more rapidly than would otherwise be practi cable. The material used for this purpose, i.e., for stiffening the layer of slip, may be applied in liquid form to the surface of the screen by any suitable means or the screen may be given a coating of a suitable plastic with which the stiffening compound may be mixed.

The mechanism described may be so adjusted that the resulting metal sheet may be extremely thin, for instance, .005". The screen itself may be varied in construction although a screen of thin porous stainless steel is eminently satisfactory. A screen of 200 mesh wire will function satisfactorily and such a screen may be conveniently coated with the stiffening compound mixed with a plastic substance.

IWhen the organic material used in forming the suspension comprises sodium or ammonium alginate the substance applied to the surface of the screen may be a salt barium or calcium with or without polyvinyl acetate. When the suspension includes monogalactan or polypectate this screen covering substance may be a salt of boron applied with or without a plastic such as epoxy resin, and when the Organic material comprises corn sugar which has been fermented, the substance applied to the screen may be chromium chloride, with or with out polyvinyl acetate. Other screen covering compounds may be utilized when different organic binder materials are employed in creating the suspension, the objective being, as previously stated, to expedite the production of sheet material by making it possible to more rapidly advance the forming screen while producing a continuous unbroken sheet at the pick-off device. It will be appreciated, however, that this method of insuring that formed sheets may be removed intact from casting surfaces may be employed when the casting surfaces is stationary rather than an advancing screen, the stiffening compound being, for instance, applied to a block having a flat surface horizontally disposed. Such a slip receiving member may be a block of calcium sulphate with which the stiffening compound may be mixed or upon the surface of which it may have been deposited, or a block of diatomaceous silica and a suitable binder of plastic material with which the stilfening compound has been mixed. Any layer of slip deposited upon such a stationary block may be removed and treated by heating and compression in any desired manner.

It has been shown that, by proceeding in the manner described, metallic sheets may be easily produced which sheets are of such composition that they can only be produced with great difiiculty, or not at all, by other methods. For instance, sheets such as that commonly known as X-40, containing 0.51% carbon and large percentages of cobalt (over 50%) and chromium (over 20%) as well as smaller amounts of nickel and tungsten can be made with facility by following the procedure recommended, and more rapidly than on machines not employing forming surfaces which have not been prepared in the manner herein described. Likewise, thin sheets of the alloy commonly known as Inconel-lOO containing major portions of nickel (over 70%) and appreciable amounts of cobalt and chromium and minor amounts of 4 titanium, aluminum, molybdenum, etc. may be made rapidly, relatively speaking, by the process described.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. The method of producing a metallic sheet by slip casting which comprises preparing the slip receiving surface of a supporting member by the application to that surface of a salt and thereafter depositing thereon a quantity of a slip which comprises powdered metal uniformly dispersed in a suspending medium which will coagulate and stiffen when it is brought into contact with said salt covered surface, whereby its ultimate removal as a sheet from said surface is facilitated.

2. The method of claim 1 in which the suspending medium for the powdered metal includes ammonium al- '7 ginate and the salt applied to the receiving surface is a salt of barium or calcium.

3. The method of claim 1 in which the suspending medium for the powdered metal includes monogalactan and the salt applied to the receiving surface is a salt of boron.

4. The method of claim 1 in which the suspending medium for the powdered metal includes polypectate and the salt applied to the receiving surface is a salt of boron.

5. The method of claim 1 in which the suspending medium for the powdered metal includes fermented corn sugar and salt applied to the receiving surface is chromium chloride.

6. The method set forth in claim 1 in which mechanical pressure is applied to the slip deposited upon said slip receiving surface for the purpose of removing some of its liquid content.

7. The method set forth in claim 1 in which mechanical pressure is applied to the slip deposited upon said slip receiving surface for the purpose of removing some of its liquid content, the compressed slip is then heated to remove additional moisture by evaporation and is then sintered.

References Cited UNITED STATES PATENTS 3,322,536 5/1967 Stoddard -211 XR 3,335,000 10/1965 Bliss 75-214 XR CARL D. QUARFORTH, Primary Examiner.

A. J. STEINER, Assistant Examiner.

U.S. Cl. X.R. 

